1. Field of the Invention
The present invention relates to an ultrasonic diagnostic device and an image processing device, and particularly to a technique for improving a time resolution of a sequence of ultrasound images obtained at a predetermined frame rate.
2. Description of Background Art
An ultrasonic diagnostic device receives an echo obtained when ultrasound emitted from an ultrasonic probe is partially reflected on reflection points and surfaces of tissue of an object of a living body to be examined. The ultrasonic diagnostic device then performs signal processing for the received echo, and generates an ultrasound image (an echo image) for the examined object. Since the ultrasonic diagnostic device generates a two-dimensional (2D) ultrasound image of an examined object of a soft part and the like without invasion, it is widely used as a device which performs examination with high level of safety, and therefore is essential in fields such as clinical medicine.
As digital ultrasonic diagnostic devices are in increasingly widespread use, a variety of ultrasonic examinations are conducted with them.
For instance, an ultrasonic diagnostic device continuously samples ultrasound images of an examined object over a predetermined time and accumulates them to allow the operator to later closely examine a sequence of these ultrasound images and their physical quantity, such as movement of the object, and use obtained information for diagnosis.
For closely examining constantly changing movement of the object such as a heart and a circulatory organ, however, the present frame rate (e.g., 10 frames/second (fps)) used by an ultrasonic diagnostic device is not sufficient.
Methods considered to solve this problem include a method for raising a frame rate of sampling by reducing a total number of pixels constituting each ultrasound image, and density resolution of each pixel, and a method for omitting real-time processing from signal and image processing. These methods, however, reduce information amount of each ultrasound image, and so cannot improve accuracy of examination as a whole.
There is also a new technique of accurate examination by the use of an ultrasonic diagnostic device, which uses ultrasound images corresponding to different cross sections (such as a two-chamber view and a four-chamber view) of the same object (such as a heart). These ultrasound images have been generated in the same phase in a pulsation (i.e., relatively the same time in a pulsation cycle), so that examination with increased accuracy can be performed (see Japanese Patent Application No. 2001-23819).
With this technique, ultrasound images in the same phase are extracted from different sequences of ultrasound images. However, there are not always ultrasound images in the same phase within these sequences because timing with which these ultrasound images have been sampled and generated may differ from one another.
Consequently, ultrasound images generated in different phases are used as ultrasound images in the same phase, but such difference in phase results in decreasing accuracy of examination.
The present invention is made in view of the above problems, and aims to achieve the following three objects.
As the first object, the present invention aims to provide an ultrasonic diagnostic device and an image processing device capable of examination with increased accuracy by increasing an apparent sampling rate applied to an ultrasound image they generates without sacrificing a resolution of the ultrasound image and real-time performance.
As the second object, the present invention aims to provide an ultrasonic diagnostic device and an image processing device capable of examination with increased accuracy even when the devices use two or more ultrasound image sequences that have been generated in different phases as a result of difference in their sampled times.
As the third object, the present invention aims to provide an ultrasonic diagnostic device and an image processing device capable of accurately examining an object (such as a left ventricle (LV) of a heart) whose information (such as that showing a left ventricular volume (LVV)) used for diagnosis changes over time. To achieve this, the ultrasonic diagnostic device and the image processing device generate an ultrasound image corresponding to an predicted time at which the diagnostic information takes a characteristic value.
For achieving the first object, the ultrasonic diagnostic device and the image processing device generate ultrasound images through sampling, associates each of the generated ultrasound image with a time stamp, and interpolates between data of the ultrasound image to generate image data corresponding to a time at which the sampling was not performed.
The second object can be achieved by normalizing a cycle for ultrasound image data in accordance with time stamps associated with the ultrasound image data, and then performs the above interpolation between the ultrasound image data corresponding to the normalized cycle.
The third object can be achieved by predicting a time at which a left ventricular volume (LVV) becomes a minimum or a maximum, and generates an ultrasound image at the predicted time.
In more detail, the above objects can be achieved by an ultrasonic diagnostic device that generates and displays an ultrasound image containing an image of an object which is subject to examination in accordance with reflection of ultrasound. This ultrasonic diagnostic device includes: an image generating unit for successively generating an ultrasound image; a quantity extracting unit for extracting a characteristic quantity related to the object within the generated ultrasound image; a time stamp generating unit for generating a time stamp indicating a time at which the ultrasound image has been generated, and associating the time stamp with the extracted characteristic quantity to make a pair; an interpolating unit for performing interpolation using a plurality of pairs made by the time stamp generating unit so as to generate new characteristic quantities corresponding to times other than times indicated by time stamps contained in the plurality of pairs; an information generating unit for generating diagnostic information on the object in accordance with the new characteristic quantities; and a display unit for displaying the generated diagnostic information.
The above interpolation on characteristic quantities generates new characteristic quantities that each correspond to a time at which sampling was not performed, and diagnostic information based on such characteristic quantities can be generated. Consequently, the above ultrasonic diagnostic device can achieve examination with higher accuracy than conventional examination using the same frame rate as the present examination. In addition, since such highly accurate examination can be achieved by data processing such as interpolation of characteristic quantity, it costs lower than other method which increases a maximum frame rate.
Here, the above ultrasonic diagnostic device may further include: a pulsation detecting unit for detecting every pulsation related to the object; and a clock unit for measuring an elapsed time from the detection of each pulsation. Here, a time indicated by each time stamp may be an elapsed time measured by the clock unit.
For this construction, a value of the time stamp is incremented in synchronization with a pulsation of the object. This allows different sets of data that have been generated in the same phase in a pulsation cycle to be specified out of sets of data obtained at different times. Consequently, with the present diagnostic device, movements of the living body can be examined from a variety of viewpoints in synchronization with pulsations.
Here, for the above ultrasonic diagnostic device, the interpolating unit may (a) superimpose a plurality of characteristic quantities over one another within a single pulsation cycle, the plurality of characteristic quantities having been extracted over a plurality of pulsation cycles, and (b) perform the interpolation between the superimposed characteristic quantities to generate the new characteristic quantities.
For this construction, characteristic quantities over two or more pulsation cycles are normalized before interpolation. This reduces an examination error resulting from abnormal movements of the living body, signal noise, and dispersion in values of the examination.
Here, with the above ultrasonic diagnostic, before superimposing the plurality of characteristic quantities over one another, the interpolating unit may normalize the plurality of pulsation cycles to generate the single pulsation cycle by correcting time stamps associated with the plurality of characteristic quantities.
For this construction, different pulsation cycles are corrected to a pulsation cycle of the same duration, and characteristic quantities are superimposed over one another based on this corrected pulsation cycle without a phase of each characteristic quantity changed before and after the superimposition. Accordingly, highly accurate diagnostic information can be obtained.
Here, for the above ultrasonic diagnostic device, the interpolating unit may perform the interpolation using the plurality of pairs that each contain a time stamp and a characteristic quantity related to an ultrasound image in first sectional view so as to generate new characteristic quantities related to the first sectional view. The information generating unit may include: an intersecting data obtaining unit for obtaining a characteristic quantity related to an ultrasound image in second sectional view from the quantity extracting unit, and obtaining a time stamp associated with the obtained characteristic quantity from the time stamp generating unit, the first and second sectional views intersecting at a predetermined view; a data specifying unit for specifying a characteristic quantity out of the new characteristic quantities related to the first sectional view, the specified characteristic quantity being associated with a time stamp that indicates a same time as the time stamp obtained by the intersecting data obtaining unit; and a data generating unit for generating the diagnostic information by using the specified characteristic quantity and the obtained characteristic quantity.
With this construction, the diagnostic information is produced from ultrasound images in the intersecting first and second sectional views, which have been generated at different periods. This generates a characteristic quantity that is closer to an actual characteristic quantity of the object than a characteristic quantity obtained merely from an ultrasound image in a single sectional view. As a result, accurate examination can be achieved.
Here, with the above ultrasonic diagnostic device, the intersecting data obtaining unit may also perform interpolation using a plurality of pairs that each contain: (a) a characteristic quantity related to the second sectional view; and (b) a time stamp associated with the characteristic quantity, and generate a new characteristic quantity related to the second sectional view. The data specifying unit may specify a characteristic quantity related to the first sectional view, the specified characteristic quantity being associated with a time stamp indicating a same time as a time stamp associated with the new characteristic quantity related to the second sectional view.
With this construction, interpolation is performed between not only ultrasound images in the first sectional view but also ultrasound images in the second sectional view, and the diagnostic information is generated based on characteristic quantities for which such interpolations have been performed. This allows diagnostic information to be generated at shorter intervals, and therefore a peak position in a change curve, for instance, can be accurately obtained.
Here, with the above ultrasonic diagnostic device, each time the image generating unit generates an ultrasound image in the second sectional view, the data generating unit may generate diagnostic information. Each time the diagnostic information is generated, the display unit may display the diagnostic information.
For this construction, the diagnostic information is generated whenever an ultrasound image in the second sectional view is sampled, which achieves real-time diagnosis for which diagnostic information is instantaneously provided.
Here, the above ultrasonic diagnostic device may also include a volume specifying unit for specifying a maximum and a minimum of the volume in a pulsation cycle by using the volume shown in the diagnostic information.
For this construction, maximum and minimum values in each pulsation cycle are displayed. This can therefore provide, for example, useful information such as an end-diastolic LVV and an end-systolic LVV of the heart.
The above objects can be also achieved by an ultrasonic diagnostic device that generates and displays an ultrasound image containing an image of an object which is subject to examination in accordance with reflection of ultrasound. The ultrasonic diagnostic device includes: a signal receiving unit for receiving an electrocardiogram (ECG) signal related to the object; an end-time predicting unit for predicting at least one of an end-diastolic time and an end-systolic time from at least one of a past end-diastolic time and a past end-systolic time that the end-time predicting unit has specified using the received ECG signal; and an image generating unit for generating an ultrasound image at the at least one of the predicted times.
With this construction, future end-diastolic and end-systolic times can be predicted from past end-diastolic and end-systolic times, which have been specified using the action potential signal. An ultrasound image is then generated at the predicted times. As a result, a more accurate LVV of the heart in end-diastolic and end-systolic times can be calculated.
Here, the above objects can be also achieved by an ultrasonic diagnostic device that generates and displays an ultrasound image containing an image of an object which is subject to examination in accordance with reflection of ultrasound. This ultrasonic diagnostic device includes: an information calculating unit for calculating diagnostic information from the ultrasound image; a time predicting unit for predicting a time at which the calculated diagnostic information takes a characteristic value by using the diagnostic information; and an image generating unit for generating an ultrasound image for the object at the predicted time.
The above ultrasonic diagnostic device predicts a time at which the calculated diagnostic information takes a characteristic value by using past diagnostic information. The diagnostic device then generates an ultrasound image at the predicted time. This can achieve examination with increased accuracy in accordance with diagnostic information corresponding to the predicted time and times around the predicted time.
In order to achieve the above objects, the present invention may be embodied as an image processing device that includes the above units of the ultrasonic diagnostic device, or as a program including steps of units characteristic to the diagnostic device. Such program may be stored in not only ROM (read only memory) used by the ultrasonic diagnostic device and the image processing device but also a recording medium, such as a CD-ROM disc, to be distributed. The program may be also distributed via a communication network and other transmission media.